Various gravity types of prefabricated groins and breakwaters exist. Made of concrete, stones or other heavy materials, they have either solid cross-section or are formed as shell-like ridge-structures. As these heavy structures are kept in place by their own weight, costly anchoring in the seabed is avoided.
The drawback of these heavy barriers is the expensive transportation of them from factory to installation site.
Other prefabricated systems consist of light materials, such as plastic, and therefore have to be anchored. For example, British Pat. No. 1383011 presents a system consisting of a sheet which, in use, forms a ridge-like barrier anchored in the seabed.
Danish Pat. No. 121080 presents a special method of filling a closed, circular hose of flexible material with sediment pumped into the interior of the hose.
Such circular cross-section of the structure, however, is inappropriate for fulfillment of most of the above objective of the present invention. A circular-cylindrical body is unstable, as it is undermined by waves and currents.